The present invention relates to a method of archiving and a method of distributing digital documents available in several resolutions in a telecommunications network.
The invention also relates to a device for archiving and a device for distributing such documents.
More particularly, the invention aims to improve the quality of service in systems distributing multiresolution digital documents in a network with a “peer to peer” topology.
It should be stated for this purpose that a network can be termed a network with a “peer to peer” topology when the various items of equipment in this network (clients, servers) put resources in common according to an equal to equal sharing philosophy. Such networks are in contradition in particular to networks of the conventional “client-server” types in which the shared information is archived in a central server. They are used advantageously for the distribution of shared data, their storage capacity being in fact unlimited.
The document WO01/84799 (Napster) describes a system of sharing digital resources in a network with a “peer to peer” topology.
The distribution system described in the Napster document comprises a central server storing, for each shared resource on the network, a list of systems for archiving this resource.
Thus, when a client device wishes to gain access to a shared resource, it can obtain, following the sending of a request to this centralized server, the address of a system archiving this resource, and then obtain the said resource directly from the archiving system selected by the centralized server.
Unfortunately, the distribution system described in the Napster document does not propose any solution for obtaining resources requested by the client device when all the archive systems as aforementioned are out of use or out of reach, for example because they are disconnected from the network. The Napster system therefore does not provide a minimum quality of service and because of this the resource is completely unavailable to third party client systems.
In order to resolve this problem, namely to guarantee a certain quality of service in a document distribution system in a network with a peer to peer topology, the inventors first of all imagined a distribution system in which a low-resolution version of the documents was archived in a central server in the network.
During the implementation of this solution, the inventors were confronted with the problem of the obtaining, by the centralized server, of the low-resolution version of the digital document.
The document U.S. Pat. No. 5,949,551 (Kodak) proposes a system of archiving digital images in a central server in a network, this central server storing, for each image, a low-resolution version of this image, this low-resolution version being systematically supplied to the central server by the client system wishing to share the original image.
Because of its centralized character, the archiving system according to Kodak does not make it possible to take advantage of the peer to peer topology, in which the resources can be replicated on several client systems.
The client systems in a “peer to peer” network are hybrid systems, having varied processing, storage and network communication capacities, none of them being capable, at least to the same extent, of obtaining a low-resolution version of a document and supplying this to the central server.
The Kodak solution, not taking account of the aforementioned characteristics, does not allow optimum use of the resources of a peer to peer topology.